1. Field of the Invention
The invention relates to audio signal processing and more specifically to a system for musical instrument signal processing that creates customized effects through mathematical manipulation of existing effects such as amplifier or loudspeaker cabinet simulation effects.
2. Related Art
During the process of creating music, musicians have always searched for the right way to express their musical ideas. Just as a composer will use different instruments within an orchestra to express music, an electric musical instrument player will choose a variety of signal processing effects to achieve a desired sound. In most cases, the amplifier is the major contributor to the resulting sound, with each brand and model of amplifier having its own characteristic sound. For example, it is not uncommon for an electric guitarist to use several different amplifier combinations in the recording studio during a recording session to achieve desired sound effects. Two or more amplifiers may even be used at the same time to achieve desired sound effects.
Electric guitar amplifiers were introduced in the 1940s and for decades their basic design remained relatively unchanged. These analog amplifiers have evolved to add tone controls, channel switching, and analog effects including reverb, tremble, and chorus to name a few examples. Yet, the core guitar system has remained the same: an electric guitar is connected to an amplifier and then to a loudspeaker for broadcasting the sound after the audio signal from the electric guitar has been processed at the amplifier. If the guitarist wanted a different sound, he would use a different guitar, amplifier, or loudspeaker.
Eventually, guitar players began inserting additional guitar effects produced by other signal processing devices into the signal chain from the guitar to the loudspeakers to obtain a wider variety of tonal characteristics or sound effects. The first and simplest guitar effects processing devices were analog pedals inserted between the guitar and the amplifier. As they evolved, a variety of both analog and digital single effects were available to the musician either as a floor pedal or a rack mounted signal processing device. Such effects pedals and rack processors added variety in tonal possibilities that were used by many guitarists to provide a plethora of effects using processors between their guitar and amplifier. The shortcomings of this approach were evident in the overall degradation of the guitar signal passing through so many individual signal processors. Also, the amount of time it would take to switch from one sound to another by adjusting each individual processing device was a limitation for the musician.
As technology has advanced, effects processor products such as the DigiTech DSP128 (released 1987) combined many effect processors into a single programmable unit. These multi-effects processors offer an integrated digital signal processor (DSP) and a simple, single user interface that allows the musician to use a variety of signal processing setups. For example, the musician may save sounds to one of several preset program locations and recall them at will. A limitation of this type of processor, however, lies in the complexity of choosing a desired sound among the immense number of possibilities that are offered.
The current state of the art for musical signal processing known to the musician is amplifier modeling. This type of processing system combines many tone shaping effects from a multi-effects processor into a single effect that will approximate the characteristics of well-known “classic” amplifiers that guitarists or other musicians desire to use. There are both modeling guitar amplifiers and modeling signal processors. Instead of buying and using several different amplifiers, a guitarist can use a modeling amplifier to approximate the tonal characteristics provided by selected “classic” amplifiers. Some modeling amplifiers, such as the Johnson Amplification JM150 (released 1997), even allow the user to simulate using two different classic amplifiers at the same time. A modeling signal processor has the same amplifier modeling effects as a modeling amplifier but does not contain any power amplifier or loudspeakers. These devices can be used in a number of ways ranging from adding modeling capability to a non-modeling amplifier, allowing direct recording of an amplifier sound without ever having the sound be sent through speakers, and even allowing the guitarist to plug directly into a public address (“PA”) system for a completely guitar amplifier-free setup during a live performance.
Although modeling systems allow a guitarist to get to the sound of a “classic” amplifier faster by combining many control parameters into a single “model select” control, they significantly reduce the number of possible sounds that can be achieved since the user is limited to the models provided by the product. Also, another limitation is that even if the modeling amplifiers are perfect recreations of the original amplifiers, the tonal characteristics can only be as good as the original amplifier. By only modeling known physical systems, the resulting model does not take advantage of tones that can be created without the physical constraints imposed by the materials and components used to construct these systems. Because these tones are based on mathematical models, the output from the digital signal processor of each product will sound identical. The net result of this is that musicians have a dramatically reduced number of tonal possibilities to choose and that the music being performed or made with these products is less likely to be tonally diverse. What is needed is an audio signal processing system that provides various tonal processing tools to generate a virtually unlimited number of models with new tonal characteristics.